The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Blind fasteners are used in a variety of applications and particularly in aircraft manufacturing. Many different types and sizes of blind fasteners are employed in the assembly of aircraft, which are based on the materials/structures being joined and the required strength. Blind fasteners typically include of a sleeve and a stem, along with of locking mechanism if the fastener is permanent (versus temporary such as a tacking fastener). For a typical installation, the stem of the fastener is gripped by jaws inside of a pulling head, while the sleeve of the fastener is biased against an opposite side of the workpieces being joined. More specifically, the stem includes a series of annular grooves, called serrations, which are engaged by the jaws of the pulling head. As the stem is pulled away from the workpieces by the pulling head, deformation of the sleeve occurs on the blind side of the workpieces (or inside of the hole, depending on the particular type of fastener) and eventually the stem fractures, leaving a portion of the stem and a deformed sleeve securing the workpieces together. Additionally, a locking ring is installed, which locks the fastener in an installed position.
Pulling heads are generally comprised of a draw-bolt system that contains a set of jaws to grip the blind fastener and pull its stem. In aerospace blind fastening systems, the gripping force provided by the jaws is important for proper fastener installation. If the force is too low, slippage of the fastener occurs and leads to installation failures, while too much force causes difficulty in using the pulling head, which leads to productivity and tool wear issues.
Additionally, multiple types of pulling heads are provided depending on the application and access limitations. For example, there exist straight, offset, and right-angle pulling heads, which have limited adjustment capability, both in terms of the jaw gripping force and the rotational position of the pulling head relative to the workpieces.